This invention relates to a drive shield for use in forming underground tunnels, mine galleries or other elongate underground excavations, and the terms "tunnel" or "tunnelling" should be construed throughout this specification accordingly. The invention is particularly useful for driving the galleries (or roads) of underground mine workings.
A tunnel drive shield is known having a plurality of elongate drive members (or knives) carried by a support frame. The knives are positioned in a parallel side-by-side relationship to define a wall-contacting shell. The knives can be advanced, individually or in groups, relative to the support frame by means of hydraulic rams. The support frame of this shield is constituted by two components which are pivotably interconnected at the roof and carried by hydraulic props. The frame components are also connected together at the floor by means of a beam whose length can be varied by means of hydraulic rams. (See British Patent Specification No. 1463194).
Another known tunnel drive shield of this general type has a support frame having a pair of foot segments engageable with the tunnel floor, and a plurality of main segments which can be braced outwardly, by means of hydraulic rams, towards the tunnel walls. The main segments are connected to their foot segments by means of telescopic guides, and the hydraulic bracing rams are arranged to apply their bracing forces roughly in the axial direction of the telescopic guides. The foot segments of the support frame are provided with floor skids, on which the entire shield is supported. (See U.S. Pat. No. 4,173,421).
The disadvantage of these known tunnel drive shields is that it is very difficult to assemble and dismantle them in the constricted space of underground tunnels or galleries. In practice, the assembly and dismantling of such shields necessitates special underground work chambers whose cross-sections are considerably greater than that of the tunnel being formed. The provision of these large work chambers results in a considerable amount of extra work, and involves additional high costs. Moreover, it leads to excessively long assembly and dismantling times.
The aim of the invention is to provide a tunnel drive shield which can be assembled and dismantled within the cross-section of the tunnel being driven.